Security systems are known for use in detecting breakage of a frangible glazing pane, for example, a glass windowpane in a motor vehicle. Such systems typically include means for detecting breakage of the pane and means for responding to such breakage, for example, by sounding an alarm or disabling the motor vehicle power train.
Complex electronic shock sensors have been suggested for detecting vibrations corresponding to glass breakage, such as in U.S. Pat. No. 3,863,250 to McCluskey, Jr. For use in a motor vehicle, however, such vibration detection systems involve undesirably high costs in producing the shock sensors and attaching them to each glass pane in the vehicle.
Alternative security systems have employed electrical continuity loss detection circuitry. In such systems a conductive coating or strip is formed on or in the glazing pane. In U.S. Pat. No. 3,609,739 to Walter, a glazing security system employs an electrically conductive strip forming a closed loop around the outer perimeter of the glass pane. Such full perimeter strips, however, present appearance problems for motor vehicle windows and, in addition, present an unacceptable risk of accidental disruption of the electrical continuity of the strip by scratching or the like, due to the extent to which it is exposed to view and unintended contact. Such security systems are further disadvantaged by the need to form or apply the conductive material prior to installing the glazing pane into the motor vehicle body. This can add considerable complexity and cost to the installation of motor vehicle glazing panes. Also, repair of the security system due to accidental disruption of the electrical continuity of the conductive coating or strip may require replacement of the entire glazing pane.
It is an object of the present invention to provide a motor vehicle glazing security system and certain componentry for such a system, which is economical to produce in the context of motor vehicle assembly and has good aesthetic qualities. It is a further object of at least certain preferred embodiments of the invention to provide a motor vehicle glazing security system, or componentry for such a system, having good durability over prolonged use and good repairability properties. Further objects and features of the invention will be apparent from the following disclosure and detailed description of preferred embodiments.